In order to facilitate mounting of a traction hook, JP4454121B2 discloses a guide ring with a tapered inner peripheral surface attached to an outer end surface of a bumper beam. A traction hook can be inserted through the guide ring and a threaded hook end can be fastened to a nut mounted to an inner bumper member. A tapered part of the traction hook is brought into contact under pressure with an inner peripheral surface of the guide ring.
Since the traction hook, described in JP4454121B2, comprises a tapered part the hook can be guided into the hole, which may facilitate mounting. Thanks to the relatively large distance between the inner bumper member nut and the guide ring attached to an outer end surface of a bumper beam, the mounting arrangement may provide sufficient support to withstand bending forces transferred via the hook when towing.
Since a length of the tapered surface is relatively small, bending forces acting on the hook will be distributed to both the outer and inner attachment parts. Since an angle between a center axis of the hook and the tapered part of the hook is relatively large, bending forces will also result in a relatively large pulling force in the inner bumper member nut.
The fraction hook described in JP4454121B2, comprising a relatively long cylindrical member between the inner support and the outer support, may be advantageous to use in some applications, such when no particular restrictions of bumper design exists.
WO2012140930A1 suggests a similar attachment for a towing hook. The hook comprises an inner threaded part, to be fastened to an inner nut member, and an outer cylindrical part, which receives some bending support from a washer arranged around a through hole in an outer bumper part. The hook comprises a small tapered portion, which acts like a stop against an outermost circumferential edge of the inner nut member in a longitudinal direction. In WO2012140930A1, bending forces acting on the hook are distributed to both the inner and outer attachment points, and as in JP4454121B2, a relatively large distance is required between the inner and outer attachment points, for providing sufficient support to a hook subjected to bending forces.
U.S. Pat. No. 7,472,919 B2 refers to a detachable tow hook assembly for vehicles. A bayonet end of the tow hook is inserted into a vehicle bumper receptacle and rotated to a locking position, for retention in place during towing of a vehicle. When the hook has been rotated, and no pushing force is acting on the hook, a spring member is pushing the hook outwards again until a bayonet member is in contact with an inner portion of receptacle walls. Bending forces acting on the hook in U.S. Pat. No. 7,472,919 B2 are distributed to an outer member of the bumper.
The hook arrangements mentioned above may be suitable in some situations, but improvements in the field of vehicle towing devices and vehicle structural members for receiving towing devices are still desirable, in particular if vehicle towing devices and vehicle structural members are subjects to new requirements concerning e.g., deformation or safety.